High strain rate effect on tensile ductility and fracture of AM fabricated Inconel 718 with voided microstructures Articles uri icon

authors

publication date

  • October 2021

start page

  • 109908

end page

  • 109926

volume

  • 208

International Standard Serial Number (ISSN)

  • 0264-1275

Electronic International Standard Serial Number (EISSN)

  • 1873-4197

abstract

  • The paper describes Electromagnetic Ring Expansion Tests (ERET) performed on Laser Melting Powder
    Bed Fusion (LPBF) Inconel 718 stress relieved test pieces, to establish the effect of a randomly dispersed
    spherically voided microstructure on tensile ductility, fracture, and fragmentation at high strain rate
    (10-3 < e < 104 s-1). An empirical model to predict porosity type and growth rates as a function of laser
    energy density was established, to select the LPBF process parameters to fabricate test pieces under stable
    conduction and keyhole melting. The size, shape, distribution of macro and keyhole pores in the test
    pieces obtained for ERET testing were characterised. At high strain rate the number of ring fragments
    for the highest porosity doubled, accompanied by a reduction in true strain at maximum uniform elongation
    and fracture strain. The trend for reducing fracture strain with increasing porosity at high strain
    rate was described by a decaying power law. Overall, there was a significant positive strain rate effect
    on tensile ductility at lower porosities attributed strain rate hardening (Hart, 1967) [1]. Fracture surfaces
    containing the highest porosity identified four different void coalescence mechanisms that helped
    explain the influence of larger pores on the stress state in the alloy.

keywords

  • electromagnetic ring expansion test; inconel 718; keyhole porosity; laser melting powder bed fusion; stable conduction porosity